Hydraulic variable pitch propellers



April 26, 1960 J. A. CHILMAN Y 2,934,154I

HYDRAULIC VARIABLE FITCH PROPELLERS 2 sheetssh eet 1 Filed Sept. 3, 1957 April 25, 1950 J. A. CHILMAN 2,934,154

` HYDRAULIC vARIABLE FITCH PROPELLERS Filed sept. s, 1957 2 sheets-'sheet z F/GJ?.

HYDRAULIC VARIABLE PrrCH PRoPELLERs John Alfred Chilman, Gloucester, England, assignor to Rotol Limited, a British company Application September 3, 1957, Serial No. 681,644

Claims priority, application Great Britain December 18, 1956 8 Claims. (Cl. Uil-160.32)

This invention relates to hydraulic variable pitch propellers of the kind, hereinafter referred to as of the kind described, comprising pitch stop means in the propeller hub operative to prevent the propeller fining oif below a predetermined pitch, and pitch stop retaining means in the hub displaceable from an operative position to render said pitch stop means inoperative.

With a propeller of the kind described, when it is required to tine oi the propeller to a pitch less than said predetermined pitch, the stop retaining means is displaced so as to render the stop means inoperative. The propeller may then be adjusted into the required pitch.

The object of the present invention is to provide, in combination with a propeller of the kind described, a warning system for indicating to the pilot the fact that the pitch stop means is inoperative under conditions in which it should be operative, for example, due to failure of the pitch stop means.

Generally the warning system comprises a uid pressure operated switch outside the propeller hub, conduit means for communicating said switch with a source of hydraulic uid under pressure to operate the switch, and hydraulic valve means in the propeller hub, said valve means communicating said switch with a bleed to relieve the pressure of fluid in said switch only when said stop retaining means is in its operative position, said switch being operable only when the pressure of uid in the switch is unrelieved through said bleed.

With a warning system as just defined, the pressure operated switch is operated when the stop retaining means is displaced from its inoperative position, for example, following a failure which results in the stop retaining means being so displaced. p

The pressure operated switch is used to control a pilots indicator, and this may be done without complications since the switch is located outside the propeller hub, and does .not therefore rotate with the propeller.

The switch is also operated when the stop retaining means is intentionally displaced from its operative position, and, according to the arrangement which is adopted, the indicator may then indicate to the pilot that the stop means has been rendered inoperative. The primary object of the indicator is, however, to provide a warning if the stop means becomes or remains inoperative due to some failure of the propeller.

It is of course necessary to make special arrangements for leading hydraulic uid into and out of the propeller hub, but this is necessary in any case with a propeller of the kind described.

Two embodiments of the present invention will now be described, merely by way of example, with reference to the accompanying drawings in which:

Figure 1 shows diagrammatically one propeller having a warning system in accordance with the invention, and

Figure 2 shows diagrammatically a further propeller v having a warning system in accordance with the invention.

Referring to Figure 1, the propeller proper is generally indicated at 11 and comprises a hub 12 which carries propeller blades 13 which are adjustable asvto their pitch in known manner by a hydraulic pitch change motor 22, 23 housed in the hub 12. The pitch adjustment is controlled by a constant speed unit of known construction generally indicated at 14. The unit 14 comprises a speed governor 15, a valve 16 and a governor pump 17, the latter having in association therewith a relief valve 17a and a nonreturn valve 17b and being connected to pump fluid from a low pressure ysource 17e such as the lubricating oil system of the engine which drives the pro-peller.

The valve 16 controls the passage of the pressure uid from the pump 17 to the pitch change motor by way of `either conduit 18 or 19 depending upon the sense of the pitch change called for by the governor. The conduits 18, 19 communicate respectively with ducts 20 and 21 passing through the hub of the propeller and leading to opposite sides of the ram 22 of the pitch change motor, the latter being movable within the cylinder 23 to adjust the blade pitch.

When the pressure fluid from the pump 17 is delivered by the conduit 18 and duct 20 to the rearward side of the ram 22, the latter is moved towards the left in the drawing to move the blades in the pitch ining direction. Movement of the ram 22 in the pitch ining direction beyond a certain point is prevented by a stop means 25. The stop means 2S comprises ashoulder at the end of 'each of a number of circumferentially spaced spring fingers 26. The fingers 26 urge the shoulders 25 radially outwardly and into the path of the portion 27 of the ram 22. The ram may, however, Vupon movement with respect to the cylinder 23, urge these shoulders inwardly when a stop retaining means iu the form of a ring 23 has been displaced forwardly from a iirst position in which it is shown inthe drawing to a second or inoperative position, but will be unable to do so when the ring 28 is in its first or operative position in which it holds the shoulders out in the path of the portion 27. The ring 28 is provided with at least one step 28a and is normally urged, by a coil spring 29, into its operative position (as shown in the drawing) in which the maximum diameter of the ring lies radially within the shoulders 25. The shoulders 25 form a fine pitch stop and when it is desired to move the blades to a pitch less than determined by the line pitch stop, it is necessary to displace the ring 28 to its inoperative position.

To this end the ring 28 is supported for sliding move- `ment upon a core part 30 of the hub structure. Forward of the ring 28 and supported for sliding movement upon Vthe core part is a piston and rod assembly 31, the latter coupled in convenient manner to the ring 28 such thatv forward movement of the piston and rod assembly 31 results in corresponding movement of the ring 23 against the effort of the coil spring 29. Y

A duct 32 which is separate of the ducts 20, 21 for supplying the pitch change motor, and which is more generally referred to as the third'oil way passes through the core part 30 of the hub and communicateswith the chamber to the rear of the piston 31, while a tap-ping from this duct is taken to an annulus 33 formed in the core part and surrounded by the ring 28. An annular recess 34 is formed on the inner diameter of the Vring 28, this being arranged such that when the ring is holding the shoulders 25 out in their extended position thereby providing the iine pitch stop, the annulus 33 is in communication with a bleed in the form of a drain passageway 35 adjacent to it in the core part. On forward movement of the ring 28 such communication is however prevented. It will be seen therefore that the recess 3d forms a valve means in the propeller which connects the duct 32 with the bleed 35 when the ring 28 is in its first position but disconnects the bleed from the duct 32 when the ring 28 is displaced to its second position.

gaats/i v The discharge side of the pump 117 is connected by a conduit 36 with a solenoid-operated valve generally indicated at 37. A conduit 3S is taken from this valve to a control valve means generally indicated at 39, while a further conduit 40 is taken from the valve 37'through a non-return valve 41 to drain. When the solenoid 37a of the valve 37 is de-energised conduit 3g is placed in communication with conduit 40 while when the solenoid is energised conduit 3S is placed in communication with conduit 36 and the drain conduit 40 is closed. The control valve means 39 comprises a valve 39a which is operated by a piston 42, the latter moving to the right in the drawing when pressure duid is delivered through the conduit 38, and opening a chamber 43 to a conduit 44 taken from this valve through a conventional transfer mulf XX to the duct 32. A conduit 45 is taken from the delivery side of the governor pump 17 to the chamber 43. When the valve 39a is opened, by displacement of the piston 42, a drain valve 39h is closed and vice versa. A further conduit 46 is taken from the left hand side. of the drain valve 39b and this connects with conduits 47 and 48 leading from the constant speed unit 14 to the suction side of the governor pump 17.

A restriction 46a is incorporated in the conduit 46 while a relief valve 49a set at say 2S lbs/sq. in. is incorporated in a conduit 49 led from conduit 46, conduit 49 communicating thereafter with drain and with the underside of the piston 50 of a piston and cylinder unit 51 of a pressure operated switch. A coil spring 51a of desired characteristics is provided beneath this piston while the upper side of the piston is in communication with the conduit 46 by means of a conduit 52. The piston Si) carries a rod 50a which extends through a sealed aperture at the upper end of the cylinder, and at its eX- tremity carries a member 53 which together with a pair of contacts forms a switch for an indicator light circuit.

. It is arranged that when the piston 50 is in its loWermost position, this when the presure above the piston reaches 15 lbs/sq. in. the switch is operated, that is to say, closed.

In operation, constant speed control of the propeller blades 13 by the unit 14 is effected inwell known manner, movement of the blades towards fine pitch being limited by the stop means 25 which projectpinto the path of the portion 27 of the pitch change ram 22.

It is essential, however, that the stop means 2S should not be rendered inoperative whilst the aircraft is in flight, as over-speeding of the propeller, with the risk of serious damage, might then occur.v Therefore if for any reason, e.g. a broken spring 29, the stop retaining ring 28 moves forwardly, it is most desirable that the pilot should have K light.

an immediate indication of this so that remedial action can be taken before, or as, the pitch change ram 22 drifts Abelow the normal operating ne pitch limit determined by the stop means 25. Such indication isalforded in the propeller now being described in the manner which will now be described.

When the ring 2S is in its operative position vas shown in the drawing the annular recess 34, the annulus 33 and thus the duct 32 and the conduit 44 are in communication with the bleed passage 35. Under these conditions the solenoid valve unit 37 is ciosed to the conduit 36, but places the conduit 38 in communication with the drain conduit 40, the solenoid 37a being de-energised. Thus the piston 42 is in its left hand position in the drawing, and therefore valve 39a is closed onto its seating, but drain valve 3% is open and places the conduit 44 in communication with the conduit 46. The relief valve 49a is closed and since the conduits 46, 44, duct 32 and annulus 33 are all in communication with the bleed passage 35 through the annular recess 34, the pressure in the cylinder Si acting upon the upper face of the piston 50 is small, the pressure in the cylinder being relieved through the bleed passage 35. The purpose of the restriction 46a is, under these conditions, to reduce the pressure in line 46 below the inlet pressure to the pump 17y and to a small value. For example the restriction may be designed to pass a ow of 100 pints per hour. The spring 51a is designed to maintain the pressure operated switch open under these conditions, that is to say the spring 51a is strong enough to prevent pressure fluid passing the restriction 46a and acting in the cylinder 5l from closing the pressure operated switch so long as the pressure in the cylinder 51 is relieved through the bleed passage 35.

if now forward displacement of the ring 23 occurs due for example to some mechanical failure, the annular recess 34 will no longer register with the bleed passage 35, the right-hand part of the bore of the ring 23 closing this over. Consequently, a pressure build up in the annulus 33, duct 32, conduit 44 and conduit 46 occurs since these are in communication through the bleed 46a with the inlet side of the governor pump 17 which receives fluid from the engine oil system at, for example, 70 lbs/sq. in. As the pressure builds up the piston 58 moves downwardly against its coil spring 51a and when a pressure of 15 lbs/sq. in. is attained the indicator switch is closed and an indicator light 53a comes on.

In addition to indicating stop failure when the propeller is operating above the tine pitch stop, the arrangement described will function under normal operating conditions to indicate that the control valve means 39 has in fact moved to its operative position when the solenoid 37a has been energised, e.g. upon touch down of the aircraft. Before such operation of the valve means 39 occurs, the pressure in the conduit 44 will be approaching zero, but as soon as the valve 39a has opened and the valve 39h closed, pressure build-up in the line 46 wili cause the indicator light to be switched on. At the same time, of course, the full delivery pressure of thepump 17 will be applied into the conduit 44 and thence'to the duct 32 to displace the ring 23 to its inoperative position and permit the blades to move to a superne pitch. If, however, during normal operating procedure the solenoid valve unit 37 fails to operate to initiate movement of the propeller blades to superflue pitch, the piston 42 will not be displaced to the right inthe drawing, andA therefore uid under pressure will not pass from the delivery side of the pump 17 to the conduit 44 and the duct 32, and the indicator will not This will however suggest failure of the solenoid, or rupture of the conduit 3S. Alternately, failure of the light to come on could indicate jamming of the piston 42.

Figure 2 illustrates a propeller having a first pitch stop meansbperative to prevent the propeller iining o below a first kpredetermined pitch and second pitch stop means operative to prevent the propeller lining off below a second predetermined pitch less than said first predetermined pitch. ln Figure 2 parts corresponding to parts already described with reference to Figure l are indicated bythe same reference numerals as are used in Figure l.

In Figure 2 the propeller proper, that is to say the rotating hub part of the propeller, is constructed and arand 7l on the ram.

ranged as fully described in the specification of copend- Aing application Serial No. 671,783, tiled on July l5,

i957, with reference to Figure 1 of the drawings of the speciiication filed with that application.

Thus, in this case, the ram 22 has a first shoulder 76, corresponding to the shoulder 27 previously described, and a second shoulder 71 which .co-operates with the shoulders 25 to form the second stop means.

The ring 28 in this case is provided with three steps 72, 73 and 74, and when the ring is in its first position with the shoulders 25 engaged on the step 72 the shoulders 25 lie in the path of movement of both shoulders 70 p When the ring 28 is displaced forwardly to a second position in which the shoulders 25 engage on the step 73 the shoulders 25 lie out of the path of movement of the shoulder 70 butin the path of movement of the shoulder 71. Thus it will be seen thatl when the shoulders l25 are on the step 73 the first stop means is inoperative but the second stop means remains opera-- tive. The ring 28 is, however, displaceable from its second position to a third position in which the shoulders 25 are engaged upon the step 74. In this position the shoulders 25 lie out of the path of movement of both shoulders 70 and 71 on the ram and the second stop means is inoperative.

Hydraulic jack means 75 is provided this jack means being operable to displace the ring 28 from its tirst to its second position. The propeller also comprises second jack means 76 operable to displace the ring 28 from its first to its third position, or, if the ring is in its second position, from its second to its third position. The jack means 76 is operable by hydraulic fluid under pressure supplied into the propeller hub through the third oilway 44 and 32 when the hydraulic valve means 39 is operated by energising the solenoid valve unit 37 aspreviously explained.

'Ihe jack means 75 is operable by line pitch fluid pressure, the jack means 75 being communicated with the fine pitch conduit 20 by a valve 77 when the valve 77 is displaced forwardly in the drawing by fine pitch uid pressure in excess of the normal operating maximum value.

A relief valve 78 controls the pressure in the conduit '18 communicating with the fine pitch conduit 20, and the relief valve 78 comprises a piston and cylinder assembly, the piston 79 of which is displaceable to gag the relief valve.

Hydraulic fluid under pressure to displace the piston 79 is supplied to the cylinder of the piston and cylinder assembly from a solenoid operated valve unit 80 corresponding in construction to the valve unit 37.

The valve unit 80, when de-energised, communicates the cylinder of the piston and cylinder assembly with the drain conduit 40. When the valve unit 80 is energised, however, the cylinder of the piston and cylinder assembly is communicated with the discharge side of the pump 17 through the conduit 36.

In operation, when it is required to render the first stop means inoperative, the constant speed unit 14 is set to fine off the propeller to a pitch setting less than that determined by the first stop means, and at the same time the solenoid valve unit 80 is energised. Energisation of the valve unit 80 causes displacement of the piston 79 to gag the relief valve 78 so that the pressure of fluid in the tine pitch uid conduit is able to rise above its normal operatingy maximum Value, that is to say the value at which the relief valve 78 would normally open. When the shoulder 70 comes up against the shoulders 25, the forward movement of the ram 22 is halted and the pressure of uid on the line pitch side of the ram is able to build up above the normal operating maximum value. It is arranged that this increased pressure, which is communicated to the valve 77 through the conduit 81, is able to displace the valve 77 into its position communicating the jack means 75 with the fine pitch fluid conduit. The ne pitch uid pressure then actuates the jack means 75 to displace the ring 28 from its rst position to its second position.

Displacement of the ring 28 from its second position to its third position is achieved by operation of the jack means 76 in the manner previously explained. In this case, however, the solenoid valve unit 37 communicates with the conduit 38 through the solenoid valve unit 80 so that the valve means 39 is operated when the valve unit 37 is energised only if the valve unit 80 has previously been energised.

In the present case it will be seen that the relief valve 49a communicates with the pressure operated switch S1 through the valve means 39 instead of directly through the conduit 46. This is, however, a distinction without a difference.

In the present example the recess 34 in the ring 28 communicates the annular recess 33 in the core 30 with a bleed passage S3 when the ring 28 is in its rst positio'i The bleed passage 83 communicates through the forward cylinder of the jack means 75 with the drain conduit 35 previously described, and the recess 33 communicates with the third oilway, also as previously described.

When the propeller is operating in a pitch change range above the first stop means, and the valve units 37 and 80 are de-energised, the pressure operated switch 51 is communicated through the conduit 46, the valve 39, the conduit 44, the third oilway 32, the recess 33 and the recess 34 with the bleed passage 83, and therefore with the drain channel 35, and the pressure of uid in the switch 51 is therefore relieved and is unable to rise to a value sufficient to operate the switch. The recess 34 is of suicient axial length to communicate the recess 33 with the bleed passage 83 only when the ring 28 is in its rst position. If

therefore the ring 28 is inadvertently displaced forwardly from its position as shown in Figure 2, communication between the recess 33 and the bleed passage 83 is interrupted and pressure is able to build up in the switch 51 to operate the switch to indicate to the pilot that at least the rst stop means is no longer effective.

In a similar manner when the ring 28 is` displaced from its first to its second position b y operation of the jack means 75 the switch 51 is operated to indicate to the pilot that the rst stop means has been rendered inoperative.

It will be appreciated that in the case of the propeller just described, by suitably lengthening the recess 34 in the axial direction it may be arranged that the pressure operated switch 50 remains in communication with the bleed passage 83 when the ring 28 is displaced to its second position, communication between the recess 33 and the bleed passage 83 being interrupted only when the ring 28l is displaced to its third position. In these circumstances the pressure operated switch 51 will operate not only to indicate inadvertent displacement of the ring 28 to its third position but also operation of the valve means 39 in the manner previously explained.

By communicating the switch 51 with the valve means 39 through an annular recess formed in the piston 79 it may alternatively be arranged that the switch 51 be operated when the relief valve 78 is gagged thereby to indicate that the relief valve has been gagged.

I claim:

l. A warning system for an hydraulic variable pitch propeller comprising a hub carrying variable pitch blades, pitch stop means in the hub operative to prevent said blades ning olf below a predetermined pitch, and pitch stop retaining means in the hub displaceable from an operative position to render said pitch stop means inoperative, the system comprising a fluid pressure operated switch outside said hub for controlling a warning device, hydraulic luid conduit means for communicating said switch with a source of hydraulic fluid under pressure sufficient to operate the switch, a Huid bleed in said hub for bleeding fluid from said switch to prevent the operation of the switch by uid under pressure from the uid pressure source, hydraulic valve means in said hub operatively associated with said pitch stop retaining means, and duct means extending from within said hub to the outside of said hub for communicating said switch with said bleed through said hydraulic valve means, said hydraulic valve means being adjustable by said pitch stop retaining means to close off said bleed from said switch whenever the pitch stop retaining means is displaced so as. to render said pitch stop means inoperative.

2. A warning system as claimed in claim 1 further corn-- prising a relief valve for said uid pressure operated switch.. said relief valve being set to open to relieve the pressure in said switch when the pressure in said switch rises to a pre-` determined value in excess of the pressure required to operate the switch.

3. A warning system as claimed in claim l, wherein` said pitch stop retaining means is in the form of a ring.;

slidable on a core in the propeller hub, said hydraulic valve means comprises an annular recess in the inner periphery of the ring, and said bleed comprises a passage in said core which passage opens into said recess when said stop retaining means is in its operative position.

4. A Warning system for an hydraulic variable pitch propeller comprising a hub carrying variable pitch blades, pitch stop means in the hub operative to prevent said blades lining ol below a predetermined pitch, and pitch stop retaining means in the hub displaceable from an operative position to render said pitch stop means inoperative, the system comprising a uid pressure operated switch outside said hub, a warning indicator connected for operation under the control of said switch, hydraulic uid conduit means for communicating said switch with a source of hydraulic iiuid under pressure suiiicient to operate the switch, a duid bleed in said hub for bleeding iluid from said switch to prevent the operation of the switch by uidunder pressure from the fluid pressure source, hydraulic valve means in said hub operatively associated with said pitch stop retaining means, and duct means extending from within said hub to the outside of said hub for communicating said switch with said bleed through said hydraulic valve means, said hydraulic Valve means being adjustable by said pitch stop retaining means to close off said bleed from said switch whenever the pitch stop retaining means is displaced so as to render said pitch stop means inoperative.

5. In an hydraulic variable pitch propeller comprising a hub carrying variable pitch blades, an hydraulic pitch change motor in the hub and operatively connected to adjust the pitch of said blades, hydraulic uid supply conduits for supplying said pitch change motor, pitch stop mea-ns in said hub operative to prevent the blades fming off below a predetermined pitch, pitch stop retaining means in said hub displaceable by hydraulic uid under pressure to render said pitch stop means inoperative, duct means separate of said fluid supply conduits for supplying hydraulic fluid under pressure from outside the hub into the hub to said pitch stop retaining means to displace said/pitch stop retaining means thereby to render said pitch stop means inoperative, and control valve means outside the propeller hub for controlling the supply of hydraulic fluid under pressure into said duct means, said control valve means having one position in which it is set to supply said duct means, a warning system for indicating that said pitch stop retaining means is displaced, said system comprising a fluid pressure operated switch outside the propeller hub, a warning indicator connected for operation under the control of said switch, iirst hydraulic uid conduit means communicating said switch with a source of hydraulic uid under pressuresuflicient to operate the switch but insufficient to displace said pitch stop retaining means, a iluid bleed in the propeller hub for bleeding fluid from said switch to prevent the operation of the switch by fluid under pressure from the iluid pressure source, hydraulic valve means in said hub operatively associated with said pitch stop retaining means, hydraulic fluid conduit means in said hub for communicating said duct means with said bleed through said hydraulic valve means, said hydraulic valve means being adjustable by said pitch stop retaining means to close oi said duct from said bleed whenever the pitch stop retaining means is dis- VIt) placed so as to render said pitch stop means inoperative, and second hydraulic iiuid conduit means communicating said switch with said control valve means, said ycontrol valve means having a further position in which it communicates said switch with said duct means through said second hydraulic Huid conduit means.

6. In an hydraulic variable pitch propeller comprising a hub carrying variable pitch blades, pitch stop means in the huboperative to prevent said blades iining ol below a predetermined pitch, pitch stop retaining means in the hub displaceable from an operative position by hydraulic uid under pressure to render said pitch stop means inoperative, duct means for supplying hydraulic fluid under pressure from outside the hub into the hub to saidpitch stop retaining means to displace said pitch stop retaining means thereby to render said pitch stop means inoperative, and control valve means outside the hub for controlling the supply of hydraulic uid under pressure into said duct means, said control valve means having one position in which it is set to supply said duct means, a warning system for indicating that said pitch stop retaining means is displaced, said system comprising a uid pressure operated switch outside said hub for controlling a warning device, first hydraulic iluid conduit means for communicating said switch with a source of hydraulic fluid under pressure sufficient to operate the switch but insuicient to displace said pitch stop retaining means, a iluid bleed in the propeller hub for bleeding uid from said switch to prevent the operation of the switch by uid under pressure from the fluid pressure source, hydraulic valve means in said hub operatively associated with said pitch stop retaining means, hydraulic uid conduit means in said hub for communicating said duct means with said bleed through said hydraulic valve means, said hydraulic valve means being adjustable by said pitch stop retaining means to close oli said hydraulic fluid supply means from said bleed whenever the pitch stop retaining means is displaced so as to render said pitch stop means inoperative, and second hydraulic uid conduit means communicating said switch with said control valve means, said control valve means having a further position in which it communicates said switch with said duct means through said second hydraulic fluid conduit means.

7. A propeller as claimed in claim 6 wherein said irst hydraulic uid conduit means contains a restriction for reducing the pressure of uid in the conduit means to a low value, and said second hydraulic uid conduit means communicates with said first hydraulic uid conduit means downstream of said restriction.

8. A propeller as claimed in claim 7, wherein said restriction is designed to reduce the flow through said iirst said conduit means to a value of the order of pints per hour when said fluid pressure operated switch is communicated with said bleed.

References Cited in the le of this patent UNITED STATES PATENTS 2,355,039 Eves Aug. l, 1944 2,542,463 Beard Feb. 20, i951 2,605,849 Bordelon Aug. 5, 1952 FOREIGN PATENTS 742,148 Great Britain Dec. 2l, 1955 

